Pumps for replenishing the leakage flow from hydrostatic units are typically fixed displacement gerotor pumping units. These designs provide for different displacements by changing the axial thickness of the pumping unit. This requires that the pocket depth in the hydrostatic unit vary in depth to accommodate the change in displacement. Some designs achieve this same result by an intermediate piece that can accommodate this length change.
The added need for these pumps to work in either clockwise or counterclockwise rotation requires either that this intermediate member be designed to reverse the eccentricity or the eccentricity must be machined into the hydrostatic unit. The result of this is that multiple pieces are required to accommodate the change in displacement and change in rotation.
These added pieces increase the cost and complexity of the hydrostatic unit. This complexity can result in higher defect rates or higher inspection costs to insure that the correct parts or orientations have been chosen.
Fixed displacement roller vane hydrostatic units are an alternative to the gerotor pumping units. However, providing fixed displacement roller vane hydrostatic units for both clockwise and counterclockwise rotation typically requires designing a unique pump for each rotation desired. Likewise, providing fixed displacement roller vane hydrostatic units with a desired displacement requires designing a unique pump for each displacement desired.
The roller vane units have a further problem of providing sufficient inlet and outlet area at the rotor for porting fluid. Roller vane units normally provide for porting of fluid through valve plates into the area between the rollers, in a direction axial to the rotation of the rotor. Typical rotor designs are made with uniform outer edges between the rollers. These uniform outer edges can effectively limit the area available to port fluid into or out of the pump. Additionally, typical rotor designs are made with slots only large enough for receiving the rollers. This restriction on the size of the slots also can effectively limit the area available to port fluid into or out of the pump.
Variable displacement hydrostatic units are not a good solution for the deficiencies of current fixed displacement gerotor and roller vane hydrostatic units. Variable displacement hydrostatic units require additional elements for the external manipulation of the hydrostatic unit to manipulate the rotational direction or displacement of the hydrostatic unit. These additional elements are unnecessary for fixed displacement applications since these applications inherently do not require the variation of rotational direction or displacement levels once the unit is installed. Further, these additional elements increase the cost and complexity of variable displacement hydrostatic units as compared to fixed displacement hydrostatic units.
Therefore, a principal object of this invention is to provide a fixed displacement pump capable of being assembled to operate in either rotational direction.
A further object of the invention is to provide a fixed displacement pump capable of being assembled to operate at a desired fluid displacement selected from multiple displacements.
A still further object of the invention is to provide a fixed displacement pump having a rotor with improved area available to port fluid into or out of the pump.
These and other objects will be apparent to those skilled in the art.